texts:
I know that Earth rotates around the Sun in an oval route:

And I know the seasons happen, because the axis of the Earth is not vertical. I think it is 23 degree slope.

How come the distance from the sun when the earth at the closest point to the Sun has no effect and if it has effect what is it?

I can see that when it is summer on the northern hemisphere it is winter in the southern and vise versa.

Shouldn't be it is hotter time for both sides when earth is closest to sun and colder when it is furthest?


texts:
Given the magnitudes (in the i-band) of certain galaxies, I would like to calculate their stellar mass (in terms of solar masses). So far, I have calculated their absolute magnitudes and gotten to working out the mass-light ratio $M/L$ for each galaxy.

e.g. $M/L=0.563$

Values I have are the calculated $M/L$ for each galaxy, and the $i$-band apparent ($13.25$) and absolute ($-18.06$) magnitudes for the galaxy, as well as the distance ($18.44Mpc$).

From this I need to get the mass of the galaxy $M$ in terms of solar masses. Therefore I assume I first need to calculate the i-band luminosity for the galaxy in solar masses $L_i$. This is where I am stuck.

However, once I have $L_i$  next step would be ...
$$M_g = 0.563 * L_i$$

Ultimately, given these values, how would I go about estimating the stellar mass of a galaxy in terms of solar masses?


texts:
A wormhole is a sort of tunnel that could connect two points in spacetime. These are theoretical objects that have not been observed. What observational evidence could we look for to confirm (or disprove) their existence? If they do exist, what should we be looking for to find one?

This answers how wormholes could be created. This is not what I'm asking about. I want to know what observations could be done (potentially with telescopes we don't have yet) to confirm the existence of wormholes.


texts: Doppler Shift Vs Gravity Assist for Frequency Shifts from Rotating Galaxies

texts:
Frequency Shift of Light Leaving Rotating Galaxies:
Differences in Doppler Shift due to Radial Velocity
Vs
Frequency Shift due to Gravity Assist from a Rotating Galaxy

A description of estimating rotational velocity of a galaxy by measureing the relative differences in frequency of light from one side of the galaxy to the other:

https://www.haystack.mit.edu/edu/undergrad/srt/SRT%20Projects/rotation.html

Another description with references to the implication of the existence of dark matter that arises from the calculated rotational velocities of galaxies versus the observed matter in the galaxies.

https://ps.uci.edu/~observat/sites/default/files/COL_Activity_RotCurve.pdf

I have been considering an alternative to dark matter to reconcile the observed mass of galaxies and their observed rotational velocities by considering frequency shifts.

If we discount dark matter then in general the observed distribution of density of matter in a galaxy  increases the closer to the centre of the galaxy one goes.

Here is my hypothesis:

Light that is moving in the same direction as the rotation of matter in the galaxy from its source to the observer is passing between higher matter dansities towards the centre of the galaxy and lower matter densities towards the edge of the galaxy. Under these conditions the light will experience a net gravity assist as described in

https://www.planetary.org/blogs/guest-blogs/2013/20130926-gravity-assist.html

Conversely light that is moving in the opposite direction to the mothion of matter rotating around the galaxy  under otherwise the same conditions will be retarded, or redshifted by the counter gravity assist.

We already know that gravity can change the frequency of light and this is described in:

https://astronomy.swin.edu.au/cosmos/G/Gravitational+Redshift

Therfore the observed relative frequency differences between light observed from one edge of a rotating galaxy is made of of the rotational doppler shift of light cause by the rotational velicity of the lights sources of the grotating galaxy and the gravity assist/contra gravity assist caused by the light moving through the rotating mass of the galaxy itself.

If the differential frequency shift from one edge of a rotating galaxy is made up of these two component then it is not going to be a simple addition of effects.

The gravitational assist is going to be, in part, a function of the rotational velocity of the material in the galaxy along with the actual amount and distribution of mass while the doppler shift is a straight calculation based of the velocity of the lights sources.

My questions are:

Does anyone know of any research, websites or papers that discuss gravity assis impacting the properties of light as it passes through rotating cosmological structures.

Can anyone identify any significant flaws in my hypothesis?

Can anyone describe the math needed to decompose the distribution of relative frequency shift between velocity doppler and gravity assist to arrive at a rotational velocity and galactic mass.

Can anyone advise what the raminifications that this hypothesis would have on the various dark matter theories?


texts:
I see here that after a very long time into the future, "Estimated time for random quantum fluctuations to generate a new Big Bang".

This begs the question, do we speculate that our big bang was the first?  Or are we one of many in a never ending chain?  Or do I miss the point entirely (being ignorant in the subject)?


texts: How far in arc seconds is a planet from its star? The star is 12 parsecs away from earth. The planet is 1 AU from its star

texts:
I've been reading the book Welcome to The Universe by Niel De Grasse Tyson. In the tenth chapter he has mentioned "Forty light-years is 12 parsecs. A planet at 1 AU from its star, 40 light-years away, will be 1/12 of a second of arc away from the star in the sky."

Can anyone explain how he got the figure 1/12 arc seconds?


texts: What is the real position of the tidal bulge?

texts:
The wikipage on "tidal accelaeration" has this picture of the tidal bulge:

but says that:

The average tidal bulge is synchronized with the Moon's orbit, and
Earth rotates under this tidal bulge in just over a day. However,
Earth's rotation drags the position of the tidal bulge ahead of the
position directly under the Moon. As a consequence, there exists a
substantial amount of mass in the bulge that is offset from the line

On the other hand, this academical article
states the opposite:

as we move with respect to both tidal bulge and moon, the moon
crosses our meridian before we experience the highest tide.] How
early? Some books show misleading diagrams with the symmetry axis of
the tidal bulges making an angle of 30° or more with the moon. In
fact, the angle is only 3°, so the tides are late by about 24(3/360)60
= 12 minutes

through the centers of Earth and the Moon

Can you say what is the real position of the bulge? it is surely a hard fact not open to interpretations. Do you have access to sites that say where is now the moon and where is the tidal bulge?
According to the basic laws of conservation of momentum and energy, a mass moving to a greater radius should be slowed downm and if we add friction the lag of 12 minutes or more makes sense. If the highest point of the bulge is forward wrt to the vertical of the moon, can you explain what stronger force pushes the water in the direction of the spin?
I found this site that gives the position of sun and moon, but doesn't show tides

This animation, on the other hand, shows that there is no bulge
The red areas experience a rise over 1 m, the blue one a depression of over 1 m:


texts: Is there any support for the Big Crunch Theory? Could there have been a partial Big Crunch in the past?

texts:
Is there proof in either the CMB or other observed astronomical phenomena for Big Crunch?
Could there have been a partial Big Crunch maybe like a cluster of Black Holes colluding to create a disappearing zone in the Universe?


texts: How is the redshift of starlight precisely measured?

texts:
When galaxies move away from us (caused by the expanding spacetime) their light seems to show a redshift. But what is really needed for this?

What time lap is for example needed to see a difference in frequency, and how does this precisely work?

Is this also possible for gravitational waves, or are amplitudes the only solution to derive the redshift from?


texts: Earlier references of Mars' arsia mons elongated cloud?

texts:
The weird long cloud on Mars is finally revealing some of its secrets is an article by  Chelsea Gohd from space.com referencing ESA's Mars Express news. The Arisa Mons Elongated Cloud (AMEC) is basically an orographic cloud the lee of the volcano Arsia Mons which is approximately 20km high. The cloud is located in 46km height and 600km/h winds create a tail which is about 1000km long and about 150km wide. The cloud head grows before sunrise, then the tail quickly grows westwards, and the cloud evaporates before afternoon. Furthermore, ESA writes in its infographics:

A curious elongated cloud on Mars has been observed over 100 times by five different missions since 1976. Mars Express has provided new insights into its daily cycle.

I italized the issue I am after: Although I follow closely what happens in the field of extraterrestrial atmospheres, I have never heard about that cloud before Mars Express. Maybe somebody could point me to earlier publications on the matter which rely on other space crafts? Are there other, similar clouds on Mars?
Related

Why are cirrus clouds more common on Mars?


texts: Which planets, nebula, and other objects can be seen using Celestron Astromaster 130EQ

texts:
I have got a Celestron Astromaster 130EQ telescope, which lens should I use to see the various planets and nebula?

When I tried to see Mars it was only a small red dot on scope.

As per the technical description, it's got 6" mirror with 650 mm focal length.
Kindly guide me to which lens of what mm should be used to see Mars, Saturn, Jupiter, Venus, and nebula.


texts: "Esperance" rock on Mars formed by erosion or weathering? or is there any rock on Mars not formed by erosion?

texts: I was wondering if the "Esperance" rock that was found on Mars by the Opportunity rover was formed due erosion or weathering? I have been reading a lot online but I did not seem to find anything. Does anyone know a type of rock on Mars that was not formed by erosion?


texts: How is the Gould Belt younger than the sun?

texts:
Our sun is located in the Gould Belt, a  group of stars which is thought to be 30 - 50 million years old. However, the sun formed 4.6 billion years ago.

Did the belt form around us?


texts: Is a cold (3800K, or so) white dwarf still be considered/in degenerate state. Or, how can a gas be degenerate and cold?


texts:
I watched an interesting excerpt from a BBC show on the work of the McDonald Observatory in its laser measurements of the distance to the moon which are apparently accurate to within a few centimeters. The observatory used to make a measurement every day and by this means a plot of the Moon's orbit around the earth was obtained over a period of approximately 40 years from about 1970 to about 2010.

At the end of the excerpt Dr. Peter Shelus says that the measurements show that the shape of the moon's orbit is not quite as expected by "Newton's" theories, which I interpreted to mean that the orbit is non-Keplerian, but possibly he meant something else. It is hard to know because the excerpt just cuts off mid-sentence, so it is unclear what he was saying exactly.

In what way is the orbit of the moon irregular according to the MacDonald measurement series?

Also, as an aside, I notice that the observatory's funding was cut in 2009 so that these measurements are no longer being made, but two other observatories are making new series. Are these other observatories making daily measurements the way the MacDonald Observatory used to do?


texts: Determine spectral type of star from its properties

texts:
How can I determine spectral type of star, if I know all its another properties? For Example, Rigel A has spectral type B8Ia.
Rigel has temperature 12 500 K. According to Harvard spectral classification, spectral class of this star is B (10 000-30 000 K) and subclass is 8 (12 000-14 000 K), so B8.
Are there any exact boundaries for Yerkes spectral classification as well? How can I tell if a star is super giant (I), bright giant (II) or giant (III)? And then, how can I tell if it is bright (a), normal (ab) or faint (b)?


texts: What technology is required to detect a coconut-sized sphere in Earth orbit, at average altitude of communications satellites?


texts:
As I was searching the answer to 'What comes after Black Holes', I found these two threads talking about the same thing

Do black holes die?

Can a black hole reach a limit where it can no longer attract more matter?

The answers here mention that Black holes do die but with time and they "evaporate"

What do you mean by Evaporation of a Black Hole?

How do these black holes lose their mass?


texts: How do astronomers find interesting events?

texts:
I always wondered how those tiny dots representing moving stars or whatever forming an interesting event (supernova explosions, stars being sucked into black holes etc.) get caught in the huge solid angle of $4\pi$? It seems absolutely improbable to find any such event in that big solid angle.

Do astronomers just appear lucky looking at the right place at the right time to find an interesting event, or do they use some systematic methods of finding them? Do they maybe use special software which analyzes tons of data and identifies such interesting events?


texts:
A project I'm working on involves getting data from SDSS DR12, and cross-matching it with NED, as described in Section 2 of this paper:

2.1 The sample
From the SDSS Data Release 12 (DR12, Alam et al. 2015), we extracted the first 33 643 QSOs with accurate spectroscopic redshifts (δz/z < 0.01), which span the magnitude range r = 14.667 − 22.618. We then used the source coordinates to obtain the nearest source within a 6 arc-second search radius in the NASA/IPAC Extragalactic Database (NED), which usually resulted in a single match. As well as obtaining the specific flux densities, we used the NED names to query the Wide-Field Infrared Survey Explorer (WISE, Wright et al. 2010) and the Two Micron All Sky Survey (2MASS, Skrutskie et al. 2006) databases. For each of the bands3, the photometric points which fell within ∆ log10 ν = ±0.05 of the central frequency of the band were averaged, with this then being converted to a magnitude.

(screenshot)
I can find the SDSS DR12 on VizieR, and I know there are tools for cross-matching catalogs (I have TOPCAT) but I'm not sure of what steps to follow.
Can anyone give me some guidance on how to do the cross-match as per the paper, please?


texts: Biosignatures for anaerobic or other early microbiology?

texts: What are some possible atmospheric bio-signatures for a planet with anaerobic life? or even microorganisms before oxygen builds up in the atmosphere? Would there be a way of telling if methane, etc. is possibly not from abiotic causes?


texts: how to calculate distance between galaxies in the distant past

texts:
for example, assume there is a high redshift galaxy called "A" with z=6, so how to calculate the distance between us and another galaxy B when the light left the galaxy A?

For example, say B has a redshift of 0.5, and let's assume when the light emitted from A, us and B both exist.


texts: Where is the sun relative to my lunar rover?

texts:
I'm a robotics researcher writing orienteering code for a solar-powered lunar rover.
I have two similar problems:

Given the position of a robot on the moon in lunar latitude/longitude, where is the sun? That is, which direction should I orient my solar panel to maximize incidence?
For testing purposes, I need to solve the same problem on Earth. Given Earth lat/lon, where is the sun?

To be honest, I'm not even sure what coordinate system to use to express the answer to these questions. I was considering a coordinate frame centered on the rover with East, North, and Up axes, but I'm open to a better suggestion!

So far, I've found some information about VSOP87 and ELP2000, and I've started reading "Astronomical Algorithms", but I'd appreciate help from the experts.

Edit

Here's what I've got so far. I can get the coordinates of the Earth-Moon barycenter using VSOP2013. If I can get from the barycenter to the center of the Earth, I can probably use EPS2000/82 to find the position of the Moon in heliocentric coordinates.

Sun->VSOP->Earth-Moon Barycenter->Earth->EPS2000->Moon

At very least, I think this would get me the moon coordinates in the sun frame. I'm hoping it would also give me the orientation of the Moon in the sun frame?


texts: Which measurements have shown that 2014 MU69 is red? (New Horizons' next target)

texts:
The recent NASA feature article New Horizons: Possible Clouds on Pluto, Next Target is Reddish

MU69 is actually the smallest KBO to have its color measured – and scientists have used that data to confirm the object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the solar system.
“The reddish color tells us the type of Kuiper Belt object 2014 MU69 is,” said Amanda Zangari, a New Horizons post-doctoral researcher from Southwest Research Institute. “The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”

Gizmodo elaborates on the significance of the red color:

Speaking today at the the American Astronomical Society Division for Planetary Sciences (DPS), mission scientists talked about the Pluto flyby, but they also looked ahead to the Kuiper Belt encounter. Recent observations made by the Hubble Space Telescope suggests MU69 is red—if not redder—than Pluto. MU69 is now the smallest KBO to have its color measured, and it’s our first sense of what this mysterious object actually looks like.
The reddish color of MU69, like the iconic red splotches on Pluto and its moon Charon, suggest the presence of tholin, a class of molecules that’s formed through the ultraviolet irradiation of simple organic compounds such as methane and ethane. Tholin doesn’t form naturally on Earth, but it’s abundant on the surface of icy bodies in the outer solar system. Using Hubble, scientists have confirmed that MU69 is part of the “cold classical” region of the Kuiper belt, which contains some of the oldest objects in the Solar System.

How was the "redness" of 2014 MU69 detected? The second link mentions that it is Hubble data - is it just photometric (images through different filters) or is there also spectroscopy?
I'm curious, just how red is it? What exactly are the numerical data that are being interpreted as "redness"? Is this exclusively the assumed visual appearance, or is there excess infrared as well?
Also, I wasn't sure if 2014 MU69 is considered a comet or an asteroid. So far everything I've read just calls it a Kuiper Belt Object (KBO). So I've used both tags.

above: graphic from NASA blogs. It looks like they are all red! (joke).


texts: Are there any good images of Sirius B at apastron in the Sirius system?

texts: Sirius B has a distance to Sirius A of 11 arc seconds at apastron; are there any good images of it at that point in its orbit?


texts: How do we measure the brightness of the stars?

texts: How do scientists measure the brightness of so distant stars?


texts: Which stars have been named after astronomers?

texts:
Most apparent stars have ancient names. But some of the newer (since 200 or so years) discoveries have been given the name of some prominent astronomer. Kapteyn's star is one example, and there are several more in that Wikipedia article. Edward Barnard et cetera. But there aren't too many, are there? It seems hard to get ones name attached to a star, or am I missing a bunch?

Kapteyn and his tie knot matching star

Astronomy was never easy, there's always more to see. Star namer van Biesbroeck in action with his flaring tiny red dwarf.


texts: What mechanisms limit the top speed of high altitude winds on Venus?

texts:
According to http://www.universetoday.com/36816/winds-on-venus/, the high altitude winds on Venus travel at about 100 m/s.

I don't think frictional resistance is really what's limiting the speed of the winds. Here's a possible cause of resistance to the winds moving even faster.

Venus has a single convection cell per hemisphere.
The atmosphere cools by adiabatic expansion as it rises at the equator,

then because it's colder than the low altitude air, it emits radiation at a lower rate than the low altitude air
so it heat's by absorbing radiation from the low altitude air faster than it cools by emitting radiation
so the temperature drops less rapidly with altitude than that from adiabatic expansion.

As the air at the equator rises, it cools

but then it's colder than the rest of the air at that altitude
so it resists being accelerated upward by the high pressure of the air under it.

Also because of that resistance, it rises slowly enough that it heats up from absorption fast enough to not drop further in temperature as it goes higher preventing it from exerting a stronger force of resistance to the flow of the convection cells than the driving force for the convection.


texts: Expansion of the universe and visibility of distant galaxies

texts:
The universe expands at an accelerating rate, which makes me wonder if at a certain point the speed of expansion between two points will exceed the speed of light. In that case, it might eventually become impossible for two gravitationally bound clusters of the universe to exchange light. I recall reading that future civilizations born after a certain point would be unable to observe the distant galaxies that we can now, and would have no way of knowing galaxies besides their own exist.

My question: Is this possible, and if so could it have already happened; the entire observable universe is one of multiple clusters that have since sped away from each other? Or can this be ruled out by other known facts about the history of the universe?


texts:
I'm new here, so if I've done anything wrong, please let me know.

I've been taking a look at some photometry data collected from TESS, and I encountered this light curve:

(please ignore the blue and orange lines, I was trying to run some statistical analysis on the data)

I haven't seen a light curve this curvy before, and I was wondering what this was indicative of.

I was also wondering about the spike at around time 1326, would this potentially be an outlier?

Thank you!


texts:
Today known most massive star, R136a1  weighs approximately 256 times the mass of our sun, how did supermassive black holes, with a mass of 10 billion times the sun form?

I understand, that when a star becomes black hole, its density increases, but does its mass also grow?


texts:
As an amateur with limited budget, I'd be interested in taking photos of the night sky, trying to capture more detail than human eye armed with a lens of comparable parameters to what I have in my camera normally could see. I doubt I'd ever get down to details as fine as Jupiter's moons, but I'd hope to see detail of some nebulae I have a hard time seeing through my inexpensive telescope, stars too dim to notice in less-than-perfect conditions etc. I'm interested in taking full-sky images just as well as zooms on specific objects too.

Currently, I have a lower-end SLC camera, with two lenses - good sharpness though lower aperture with 50-120mm focal length, and a wide-angle, high-brightness one (about 12-50mm) currently. Firmware hacks allow me to take photos of arbitrarily long time, and I have the remote to start and stop it without touching the camera, and generally software-wise the camera is quite powerful. One of the lenses (the longer focal length) is of "standard professional" quality level too.

Is this sufficient to get started? If so, what kind of settings should I use? If not, what other kind of entry-level equipment would I need to obtain/build on budget to get started with night sky photography?


texts: What Would it Look Like Inside Jupiter's Great Red Spot?

texts: From what I've read, Jupiter's 'Great Red Spot' is an unbelievably powerful storm. Do astronomers and scientists have any idea of what that might look like if it were possible to be inside/below it? Would it look like a storm on Earth (thunder, lightning, winds, etc.), or would it look completely different?


texts: Simple question about the phases of the Moon

texts:
If on March 20 the Moon were located at the position of the sun, how can I determine the phase in September 22, June 22, and December 20?

I drew the orbit and calculated by dividing sidereal days to get the position of moon. Then I moved the Earth to determine the position. But the answer was Full moon, First quarter, Third quarter respectively, which was different from mine.  I can’t figure out why I’m wrong.


texts: Unidentified color changing object in sky

texts: Yesterday, I was just star gazing and I noticed some star-like object moving with a high speed somewhere near the Orion's Belt and exhibiting all the seven colors i.e VIBGYOR and after a few moments, it disappeared. Any plausible explanations for this observation?


texts: I would like to obtain Tycho Brahe's data on Mars. What would be an authoritative source? One source I could find is this page (the data is given as an Excel file) but I have no idea can that be trusted. Does some astronomical organization or university keep the data public? I suppose Tycho wrote his data into a book. Where is that book located at the moment?


texts: If the moon is losing energy dragging the oceans around, why is it moving away from earth instead of falling like any other satelite would?

texts: If a satellite loses energy it starts to circle lower and finally hits the atmosphere. The moon is moving like an inch a year away from the earth even though it is losing energy pulling the oceans around.


texts: Why does this nucleogenesis table not label s and r-processes for all elements (not-labmade) past Fe?

texts: I'm reviewing nucleogenenesis and came across the table below. I like it because it actually labels the s and r-process elements, but I became confused as to why the neutron capture processes begin at A = 38. I thought anything with an atomic number greater than 26 has to be formed by neutron capture? What is my confusion here? Thanks in advance!


texts: Why don't all perseid meteors follow the same trajectory?

texts: Since these bits of debris crossing Earth's orbit have the same relative speed, why aren't they drawing parallel paths in the upper atmosphere? (consider one hour of observation to minimise Earth's rotation influence)


texts: What are some theories that explain the 11 year solar cycle?

texts: The Sun exhibits a periodic cycle for solar activity as manifested by solar activity (e.g. sunspots, solar flares). This activity is related to magnetic fields which emerge from the interior of the Sun. The magnetic fields are created by the solar dynamo. The Earth has a dynamo as well but the Earth's magnetic field is (mostly) constant in time. What is some current theories (assuming there isn't one already accepted) that explains for why the solar dynamo generates magnetic fields periodically?


texts:
In The Observatory @Donald.McLean linked to Scientists will peer at first galaxies with James Webb telescope which says in part:

Many of the proposed tasks for the Webb telescope were planned and approved in the 1990s as the observatory was under initial development, said Klaus Pontoppidan, an astronomer and Webb project scientist at the institute.
"We've just added the final projects that will be included during the first year or 13 months," Pontoppidan said.
The institute, which solicits proposals each year for Hubble, will do so for Webb, as well, and each of the space telescopes attract more than 1,000 such ideas each year, he said.
The Webb telescope will take about three months to power up, extend its massive mirror and begin observations. After that, scientists based at institutions around the world have planned more than 10,000 hours of observations with it.
Hundreds of hours
It takes an average of 25 hours to observe a single planet, but longer observations -- such as detecting the oldest and farthest galaxies -- will require about 200 to 300 hours, Pontoppidan said.
"The first galaxies in the universe, those are really faint objects, so you have to stare at them for a long time," he said.
Another big astronomy question for the telescope is to determine which came first -- galaxies or the black holes that reside at the heart of most large galaxies, said Rogier Windhorst, an astronomer and physics professor at Arizona State University.

JWST is a very different telescope and suite of instruments than Hubble and is designed to address several different questions that Hubble can't. We should not make an apples-to-apples comparison between the two.
But is a generalization on the expected durations of observations possible? Even though HST does have some famous long duration deep field exposures, many individual exposures at least have durations of only minutes.
Question: Will JWST have fewer observing sessions of much longer duration compared to Hubble?


texts: If all the Trappist-1 planets are tidally locked, which ones may have temperate zones?

texts:
Since all the Trappist-1 planets have circular orbits, it is entirely likely that all them are tidally locked.
If so, which ones of the planets may have temperate zones either on the bright or dark sides?


texts: Are the stars in constellation located in a plane or they are in different distances from each other and when we observe them from the Earth we think they are all in a plane?


texts: Let's say I am in Brasilia (latitude = 15.78°S). This is obviously south of the equator but north of the tropic of capricorn. So on the summer solstice I know that the Sun's declination is +23.26°. Does this mean that the sun will appear directly north at solar noon? Thanks.


texts: How do I find out when a constellation reached its zenith?

texts:
I found this website to look at the sky at the specific time and location: http://www.fourmilab.ch/cgi-bin/Yoursky - you can insert latitude and longitude and time to see how the skies looked at any location/time. What I need to find out is when a particular constellation reached its zenith. I see that if I change the Universal time the location of the constellation in the sky changes, but where is the zenith of a constellation? The constellation in the question is Bootes. How do I know its zenith time let's say for today? preferably using the website above.
Picture example from the website:


texts: What is the coordinate acceleration for pure radial motion?

texts:
As seen in this answer and also in this book chapter 6, page 6-10 expression 22,  when you are falling in radially from being at rest at infinity your velocity in coordinate time, as seen from a distant observer, can be described by the expression:

$$\frac{dr}{dt} = -\left(1 - \frac{r_s}{r}\right)\left(\frac{r_s}{r}\right)^{1/2}c $$

If we assume ”$r$” to be the real radial distance and not just the ”r-parameter of Schwarzschild coordinates” this is the velocity $v$. I want to know the expression for the acceleration as a function of ”$r$” and ”$v$” for a small object of mass $m<<M$ moving purely radially inwards or outwards from a compact spherically symmetric mass distribution in the general case.

By taking the derivative with respect to "r" of the expression above I get:
$$\frac{dv}{dr}=\frac{0.5}{r}{\sqrt{\frac{r_s}{r}}(1-\frac{3r_s}{r})}c$$

From these two expressions we see that the maximum velocity is $v=\frac{2}{3\sqrt{3}}c$ at $r=3r_s$. From this finding, $\frac{dv}{dt}$ should not be so hard but this will not be a general expression but only the acceleration of something dropped from rest at infinity. In Schwarzschild coordinates the radial velocity of light goes as $v_{light}=c(1-r_s/r)$. At $r=3r_s$ this becomes $v_{light}=2c/3$ so when falling in from being at rest at infinity you reach maximal velocity when $v/v_{light}=1/\sqrt{3}$. Maybe you can say that gravitation becomes repulsive whenever you are travelling towards the center of the gravitational field faster than $1/\sqrt{3}$ times the local speed of light?

Question: What does the general expression for the acceleration of an object in coordinate time look like for an object moving purely radially inwards/outwards from the center of the gravitational field assuming a spherically symmetric non-spinning mass distribution and that the r-parameter of the Schwarzschild coordinates is the real physical distance?

I am looking for an expression for the instantaneous acceleration as a function of "r" and "v".

I know that in the weak fields of our solar system Nasa/JPL are using this expression to calculate Newtonian plus relativistic acceleration:

$$\frac{d\bar{v}}{dt}=-\frac{GM}{r^2}\left(1-\frac{4GM}{rc^2}+\frac{v^2}{c^2}\right)\hat{r} +\frac{4GM}{r^2}\left(\hat{r}\cdot \hat{v}\right)\frac{v^2}{c^2}\hat{v}$$

This is based upon a first order expansion of the Schwarzshild solution in isotropic coordinates. For pure radial infall you get:

$$\frac{d\bar{v}}{dt}=-\frac{GM}{r^2}\left(1-\frac{4GM}{rc^2}-3\frac{v^2}{c^2}\right)\hat{r} $$ which becomes repulsive whenever you are approaching the central mass faster than:

$$v=\frac{c}{\sqrt{3}}\sqrt{1-\frac{4GM}{rc^2}}$$

I am hoping for an exact solution for pure radial acceleration in "Schwarzschild coordinate space" and coordinate time similar to the approximate solution for pure radial acceleration you can get from the Nasa equation.

As per the answer by amateurAstro down below the expression should be:

$$\frac{dv}{dt}=-\frac{GM}{r^2}\left(1-2\frac{v^2}{c^2(1-\frac{2GM}{rc^2})}-\frac{v^2}{c^2(1-\frac{2GM}{rc^2})^2}\right)$$

This is consistent with stuffing:

$$\gamma=\frac{1}{\sqrt{1-\frac{2GM}{rc^2}-\frac{v^2}{c^2\left((1-\frac{2GM}{rc^2})(\hat{r}\cdot\hat{v})^2+|\hat{r}\times\hat{v}|^2\right)}}}\frac{1}{\sqrt{1-\frac{2GM}{rc^2}}}$$

into

$$\frac{d(m\gamma\bar{v})}{dt}=-\frac{GMm\gamma}{r^2}$$

to get (at least this is true for pure radial and pure non-radial motion):

$$\frac{d\bar{v}}{dt}=-\frac{GM}{r^2}\left(\hat{r}-2\frac{v^2(\hat{r}\cdot\hat{v})\hat{v}}{c^2(1-\frac{2GM}{rc^2})} -\frac{v^2(\hat{r}\cdot\hat{v})\hat{v}}{c^2(1-\frac{2GM}{rc^2})^2}\left((\hat{v}\cdot\hat{r})^2+(1-\frac{2GM}{rc^2}-\frac{v^2}{c^2})|\hat{v}\times\hat{r}|^2\right)\right)$$.

(I am trying to find a velocity-dependent term that together with the classical Newtonian acceleration should reproduce Schwarzshild orbits exactly)


texts: How would light from a blue or red star affect the way we see?

texts:
How would things look if we saw them through the light of a blue or red star?
Would there be any changes?


texts: Help With Transit Radio Telescope Data Analysis

texts:
My high school teacher and I recently built a 10 ft. mesh dish transit radio telescope. In order to compete this year at Nationals for our science fair, we came up with the idea of using a bluetooth transmitter and receiver to transmit the radiowave's received from the telescope to the lab inside where my computer is located. I will be using MATLAB to take in the voltage input, analyze the radio frequencies, and create a 3D plot/image of the object were receiving from. The difference in our scope vs's other radio telescopes is its ability to rotate 360 degrees repeatedly to image the sky, taking in radio waves at different angles of ascension.

Where I'm stuck is the 3D plotting of the images. What links/articles could you think of to assist with the mathematical transformation of these radio signals into rough images. Considering the meridian circle as our basis of rotation, will the repeated persay imaging of the sky allow for an increased arcsecond of resolution due to the fact the arrays of data from each rotation will often overlap? If needed, I can draw and attach a rough image of what the radio telescope looks like. But the dish just rotates repeatedly about the horizontal axis, rather than a back and forth transit telescope, say 30 to 150 degrees and back from 150 to 30 degrees again.

What facts about astronomy, laws/theories, or anything else do you think would assist me in the creation of these images. I want to write the program from scratch, but if there is any good libraries out there to possibly write it in another language, that'd be nice to know.

Sorry if my question is too broad and kinda ambiguous. If needed I can narrow it down to a single question, but would rather not be closed due to its ambiguity.

Thanks again, and I truly appreciate any assistance, whether it's merely a URL or an in depth description, anything helps!


texts:
When I see this picture, I'm trying to understand how these two elements merged together and have two hypothesis :

two balls of lava in fusion together
two solid rocks fused at their contact point

But it appears that the collision speed was not particularly fast so I'm not sure in the end.

What process likely formed Ultima Thule?


texts: How does one measure vector magnetic field of astrophysical object?

texts:
Magnetic field strength is measured using Zeeman splitting. This is the one of the way Sun's magnetic field strength is measured. Now, how one measure vector magnetic field?
Vector magnetic field = Magnetic field and it's components.


texts:
The Wikipedia article on Sphere of influence states that:

  "A sphere of influence (SOI) in astrodynamics and astronomy is the
  oblate-spheroid-shaped region around a celestial body where the
  primary gravitational influence on an orbiting object is that body."
  (Emphasis added.)

It then gives an expression for the radius of the sphere of influence.

Is the SOI a spherical region or a oblate-spheroid-shaped region?
If it is an oblate-spheroid-shaped region, then why?


texts: How long does it take from the moment the Sun star 'touches' the horizon, to the time it totally disappear? (I'm not talking about the radiation (rays), but just about the appearance of the star by itself. I don't care of the rays). If I were near a beach or plane I'd check it, but I'm in crowded urban region so it's difficult to check it I believe).


texts: When I read that a system is located x light years away, why is there no direction?

texts: Well, I just read an article about a galaxy with two black holes, and it stated that the galaxy is 1 billion light-years away. Why is there no direction given? If the Big Bang happened, and things are moving away from each other, we can still have at least two directions - away from the center, and to it. Is that a right way to think about space and our drift in space?


texts: Issue translating World Coordinate system to cartesian coordinate

texts:
I have two fits images from the WFC3 that I am trying to combine with a C# program.  When I try to combine multiple images I don't think the values I am getting for my x/y coordinates (calculated from Right Ascension/Declination) are correct.  I am expecting a final image that is about the same width as the two images combined, but it turns out to be about the same width and about twice the height.  I know the final image should be about double the width of a single image because I manually combined the images in photoshop and the final image was about twice as wide as either of the two original images.

NOTE:  when I say "image" they are fits images, so they are just a bunch of single values in a file, so to combine them I create a new file and initialize the correct number of single values (width * height) to zero, and then fill in the values from the images I am using to combine.  They are not jpg or tif or png.

I am using the following formula to change from world coordinate system to cartesian:
formula is (since distance is the same for everything):
x = cos(dec) * cos(ra)
y = cos(dec) * sin(ra)

I get the right ascension and declination from the header in the fits file.

For the final image dimensions, I calculate the distance between x1 and x2 and create a new image that is 1/2 image 1 width + distance + 1/2 image 2 width.  For the final height I do a similar calculation with y and image heights.

The images do also have a rotational component, but I am ignoring that as both images share the same rotation.  This could be part of my problem.

public const double PixelsPerArcSecond = .039; // per WFC3 spec from Nasa

public static ImageDataModel Combine(List<ImageDataModel> inputImages)
{
    //  Right ascension is CRVAL1
    //  Declination is CRVAL2

    //  formula is (since distance is the same for everything):
    //     x = cos(dec) * cos(ra)
    //     y = cos(dec) * sin(ra)

    ImageDataModel returnImage = new ImageDataModel();
    ImageDataModel bm = inputImages[0];

    double x1, y1, x2, y2;

    x1 = Math.Cos(bm.CRVAL2) * Math.Cos(bm.CRVAL1);
    y1 = Math.Cos(bm.CRVAL2) * Math.Sin(bm.CRVAL1);

    int mult = 4; // todo: set this based off of the bitpix of the incoming images.

    for (int i = 1; i < inputImages.Count; i++)
    {
        ImageDataModel cm = inputImages[i];

        x2 = Math.Cos(cm.CRVAL2) * Math.Cos(cm.CRVAL1);
        y2 = Math.Cos(cm.CRVAL2) * Math.Sin(cm.CRVAL1);

        double dx = x1 - x2;
        double dy = y1 - y2;

        int distX = (int)((dx * 3600) / PixelsPerArcSecond);
        int distY = (int)((dy * 3600) / PixelsPerArcSecond);

        // This is what I expect to be wider than tall, but the converse is true.
        int w = Math.Abs(distX) + (bm.ImageWidth / 2) + (cm.ImageWidth / 2);
        int h = Math.Abs(distY) + (bm.ImageHeight / 2) + (cm.ImageHeight / 2);
        // This is where the two images are combined into the final image.
        ImageDataModel imd = CombineTwoImages(bm, cm, i, w, h, mult);
        bm = imd;
    }

    return returnImage;
}

I am expecting an image that turns out like this:
http://wierdling.net/stack-overflow-images/ManuallyCombined.png

But getting this:
http://wierdling.net/stack-overflow-images/CombinedTest.png

The stats for the first image are: Width = 4139, Height = 4535, RA = 350.1584456860353 (CRVAL1), DEC = 61.16155335032816 (CRVAL2), ORIENTAT = -125

The stats for the second image are:Width = 4139, Height = 4535, RA = 350.1159150008405 (CRVAL1), DEC = 61.19543100394401 (CRVAL2), ORIENTAT = -125

The final expected width is close to 7733 with a height near 4773.

The final actual width is 4284, and the height is 7662.

Does anyone have any insight into what I am doing wrong?

The full source code for the program can be downloaded from https://bitbucket.org/wierdling/fitscombiner/src/master/

It currently only works with WFC3 data, and the program is very much a work in progress.


texts: Does Tobler's First Law of Geography Apply to Star Composition?

texts:
There is a principle in Geography called Tobler's First Law of Geography which states that "Everything is related to everything else, but near things are more related than distant things."

Does this principle apply to star composition?  Do stars that are closer together have similar compositions than those that are far apart?  I'm guessing that stars that are formed in the same stellar nursery would have similar compositions.  Have studies been done to compare the compositions and proximity of stars?


texts: What if a primordial black hole went through the Sun?

texts: How much mass would the Sun lose to a primordial black hole that (initially) has 10 Earth masses, passing through or close to the center of the Sun at solar escape velocity? How massive would the Sun end up and how massive would the black hole become?


texts: Is it possible to detect gravitational lensing behind the Moon?

texts:
Eddington waited for an eclipse to happen to be able to observe gravitational lensing of the stars behind the Sun. And nowadays, amateurs can do the same thing.

Of course, the Moon is much lighter than the Sun, so it doesn't bend light as much. But since Eddington's time, our observation capabilities have greatly increased. Is it possible to detect the gravitational lensing of stars that are behind the Moon?


texts: What is meant by "revolution of Sun's apogee"?

texts:
While reading Translation of the Surya Siddhanta and of the Siddhanta Siromani(1861) - Bapu Deva Shastri, I stuck in the follwing.
Chapter I, verse 41 & 42

In a KALPA (4.32 billion years), there are 387 revolutions of the Sun's Apogee (about the earth), 204 of Mars' apogee, 368 of Mercury's apogee, 900 of Jupiter's apogee, 535 of Venus' apogee and 39 of Saturn's apogee.

Now my question is what is meant by 387 revolution of Sun's apogee? It will be helpful if someone can explain this.
This is the same question I have asked here, but as not getting proper explanation I am posting here too.


texts:
I just wanted to know if what we can only see out-side of our planet is just the past of other objects?

If 1 Light Year is equals to 365.25 Days, then I saw an object outside our planet that is 1 Light Year away from us, does it means I just saw its past 365.25 days ago?


texts: Is parallax a "technique to measure the star distances" or a "tiny shift in star's position"?

texts:
I am not completely sure whether the Parallax is a "technique to measure the star distances" or a "tiny shift in star's position"?

The a book says two points about Parallax:

Astronomers have developed a variety of clever techniques for measuring the vast distances to stars, one is called Parallax.
Astronomers can measure a star's position once and then again 6 months later and calculate the apparent change in position. This tiny shift in stars position is called its parallax.

Apart from the book source, whatis.techtarget.com defines Parallax as the way an object’s position or direction seems to change depending on viewing angle.


texts: What is the gravitational lensing focal distance of a white dwarf star?

texts:
I tried looking this up, but I couldn't find any formula on gravitational lensing distance.   I know that our Sun's is about 550 AU, though further distances work too, as it's not a single focus due to the gravitaional field diminishing over distance from the focusing body.

Is there a reasonably simple formula for calculating distance for a gravitational lens.   I'm specifically curious for white dwarf stars as there's one just 8 light years away and they see like a good object with a good lensing but not super tight focusing like a neutron star or black hole.

For example, if a telescope was built using Sirius B as a focus, how far would the telescope have to be and how powerful might it be (Maybe how powerful should be a separate question but I'll leave it here for now?

Would Sirius B's binary orbit be a hindrance or a benefit, allowing a greater area of focus?

Pure curiosity.   I don't expect we'll get there anytime soon.


texts: Io gets its volcanic heat from being flexed by Jupiter's gravity, and this seems to go on forever.  That sounds like a magic energy source, since Jovian gravity is perpetual and Io seems to remain in orbit perpetually.  Have we discovered magic?


texts: How was this interstellar fireball observed and its trajectory analyzed?

texts:
The short, interesting paper Discovery of a Meteor of Interstellar Origin describes a proposed discovery of a second interstellar object. This one hit the Earth, and was discovered not by telescope, but by "data mining" the CNEOS fireball catalog https://cneos.jpl.nasa.gov/fireballs/

It is not hard to find in the table based on the date given in the paper, but the information listed is sparse, there's no ID number or information how this was obtained:

peak brightness UTC   lat     lon    alt(km)  v(km/s)  vx     vy     vz
2014-01-08 17:05:34   1.3S   147.6E   18.7     44.8   -3.4  -43.5  -10.3

total radiated kJ   calc total imact kt
     3.1e10                0.11

Question: With what instrument was this particular fireball observed and recorded, and how was it analyzed and processed into a trajectory and state vector to be entered into this table?

  Figure 1. Trajectory of the January 8, 2014 meteor (red), shown intersecting with that of Earth (blue) at the time of impact, ti = 2014-01-08 17:05:34.

  Figure 2. Size distribution of interstellar objects based on the detection of ‘Oumuamua and of the meteor detected at 2014-01-08 17:05:34 UTC. Red lines indicate the envelope for possible power-law fits (slopes of -1.9 to -3.8), given 95% Poisson distribution confidence intervals on each number density (based on a single detection for each). The range of possible power-law slopes is consistent with that inferred for small bodies in the Kuiper belt, -2.5 to -3 (Kenyon & Bromley 2004).


texts: Where on Earth can moon rise on the meridian?

texts:
Somewhat related to this my picture showing only diurnal motion but Moon—seen from Earth—has a rapid motion with respect to the inertial celestial sphere, unlike stars and planets. Its motion relative to stars partially cancels the diurnal motion, and as the Moon’s orbit is inclined wrt Earth’s equator, Moon’s declination also changes and hence it can rise in 180°, 181°, 182°… or 360°, 359°, 358°… where objects moving only diurnally (such as stars and planets) cannot rise.
How far outside the polar circles can Moon rise in the Western celestial hemisphere or in north/south exactly? How is it best to see practically?

Also a meta request: where is a tag on astronomy.stackexchange about astronomy at high latitudes?


texts: What could be the name of a huge asteroid I watched some years ago?

texts:
Some years ago I was with my family in Venezuela. I'm not sure about the date/hour, but probably it was somewhat around 2007 in the afternoon. We were talking when one of us saw a huge meteor moving "slowly" from East to West. It was visually about 1/4 of a full moon size. It took a lot to get lost from our view (I'd say more than a minute). We could see the fireball burning and leaving the trail.

I never heard about this in the news and wanted to know if this same event is familiar to somebody else or if you've had a similar experience before.

I mean, this thing was huge and we were just waiting for it to crash but it seems we were lucky.

Edit:

It wasn't a satellite, since we could see the "rock". It wasn't like these meteors which you cannot distinguish the trace from the fireball.

I'm not sure about the date.


texts: How is the time of sunrise and sunset determined?

texts:
If I do a quick Google search for amsterdam sunrise, I immediately get the time back: 6:42 AM.

How is this time calculated?

(I mean how it is really calculated, not how Google get it, with is probably from a table. Of course I mean sunrises and sunsets in the future, not from the past. $:)$)


texts: How to discover Neptune from the Uranus orbit (by computer simulation)

texts:
I would like to demonstrate the existence of another planet (Neptune) by studying the discrepancy between the observation of the Uranus orbit and the mathematical prediction, this work was made from Le Verrier and I would like to understand his method.

I have read the Chapter 2, "The Discovery of Neptune (1845-1846)," in the biography Le Verrier -- Magnificent and Detestable Astronomer,
but it is too much in-depth and I did not understand very well his work.

I am studying the three-body problem (Sun, Uranus, Neptune) via Matlab and the two body problem (Sun, Uranus) taking the initial condition from here:

http://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html

I have tried this method:
I put Uranus in the Perihelion with the Max. orbital velocity and I calculate the semi-major axis, and it is more accurate than the one obtained from putting Uranus and Neptune in the Perihelion with their respective Max. orbital velocity.

Here a cool pic made with Matlab:

Can anybody help me? what I have to do and with what data I have to compare my prediction? Even a simple link could be helpful.


texts: What is the speed of gravitational waves ?

texts: I read that two huge black holes collided or merged and so it created gravitational waves billion years ago , So now we are able to detect it & detected it. So what is the speed of gravitational wave ? Is it faster than light ? and  are there many more to be detected ?


texts: Why does the Hubble flow does not carry photons with it?

texts: I have this naive question. We know that the expansion of the universe "takes" or "carries" the galaxies with it, separating them, but this doesn't apply to photons. My guess is that it has to do with the fact that photons are massless (i.e. they always move with c), but I am not sure and would like a more physical explanation or insight.


texts: How does a cross dispersed spectrum look like in a reality (from echelle spectrographs)?

texts:
I am an analytical chemist with some interest in amateur spectroscopy. Since astronomers use echelle spectrographs to study the high resolution spectrum of the stars, someone suggested to post the query here. An echelle grating produces a spectrum with several overlapping orders. One can then use a cross-disperser, which could be a prism or a grating, which can separate the overlapping orders and then we obtain a very high resolution spectrum. I want to know how a real echelle spectrogram looks like -as if we were looking at the 2D spectrum with our naked eyes?
I have a small echelle grating (79 grooves/mm, 75$^o$ blaze) and tried to visually generate a 2D spectrum with the help of a plastic transmission grating. The light source was an ordinary fluorescent lamp Pictures are posted below. The experiment is too elementary.  A horizontal slit made by two blades as an entrance on the shorter rectangle of a shoebox. The light from the slit falls on the reflective echelle. On the larger side of the shoebox, I made a window to take a picture.
Picture 1: A vertical slit made in a cardboard box, the long side of the echelle is perpendicular to slit An expected overlapping order spectrum seen.

Picture 2: A horizontal slit made in the cardboard box, now the long side of the echelle is parallel to the slit

Now, if we hold a plastic transmission grating (Edmund) in our hand, with its rulings perpendicular to the echelle, and view the echelle through that transmission grating, I can photograph the following 2D spectrum.
Picture 3: Hold a transmission grating with its rulings crossed with the echelle and view picture no. 2.

Unfortunately, this looks like a replica of a spectrum rather than separation of orders.
**The main question: How should one hold the transmission grating in order to visually see the separated orders. Picture no. 3, was supposedly, separation of orders but it does not look like it.
If this were a true 2D spectrum we should see some increasing distance between Hg green lines. All separated orders look the same resolution. Is there any other simple way to see a true cross dispersed spectrum with eyes using a simple cardboard type box? The key problem seems to be the issue how should we hold the transmission grating in order to see a true 2D spectrum unlike Picture 3.**
EDIT
After Prof.ELNJ's suggestion in the answer, I wanted to confirm if this is what he meant. The grating has an arrow with a pencil (from ThorLabs) which shows the blaze direction because by viewing in this direction one can see a "rainbow" of colors. So the arrow is towards the viewer, and I hold a transmission grating "crossed" with the echelle ruling.

Rough view of what appears to the eye


texts: How large (that is, radius) could a planet be?

texts:
I know that normal planets don't get any larger than Jupiter (or 2 Jupiter radii if hot), as adding more gas just increases density, not radius, until you reach the point of being a brown dwarf star.

That compressability, I suppose, is a property of the overall average material that forms star systems, as beyond a critical size it accretes the ambiant gas as well as dust in the cloud.  That is, it's mostly hydrogen and a quarter helium with a bit of other stuff.

But what about a body made of other stuff, such as rock or metal? Without worrying about planetary formation processes, just that atoms are piled together and feel self gravity. Perhaps it needs to be grown slowly so it has time to cool before adding more. Otherwise, no special techniques: just what would happen if material of suitable composition was heaped together?

I suspect that normal ideas of minerals would not exist under that kind of pressure, even if carefully allowed to cool. But can elements other than H and He still compress their volume in the same way, or would a rocky world be able to reach sizes of millions of miles?

What about more exotic cases, like the "puffy" planet I heard of that has the density of styrofoam?


texts: The Force of attraction between two bodies is proportional to the product of their masses. And considering the equation $F=ma$. Acceleration due to gravity will be more for objects lower mass. This contradicts the established theory that objects with different masses take the same time to reach the ground if dropped from the same height. Please explain


texts: Open problems in astronomy that an amateur (with a PhD in some other field) would have a chance of solving?

texts:
What are some open problems in astronomy that an amateur would have a chance of solving? Suppose the amateur has a PhD in some other field, owns a basic telescope, a set of filters, diffraction gratings, cameras, and happens to know a lot about machine learning, signal processing, spectral estimation, statistics & design of experiments, and basic physics and chemistry.

Are there better tags available (such as "research")?


texts: From inflation theory and other theories explaining the birth of the universe, the universe is expanding and recently it's been discovered that the expansion has been accelerating. My question is simple, what is happening on the boundary of our inflating universe and what is that 'space' that is experiencing that boundary?


texts: What is this gap between hot and cold Jupiters?

texts:
When plotting mass to semi major axis on exoplanets.org, there seems to be a gap between Hot Jupiters and Cold Jupiters. A lot of Jupiter-mass planets at less than 0.1 AU have been discovered, and a lot at more than 1 AU, but there aren't so many in between.

Since many planets closer and further away from their star have been discovered for the same mass, it seems unlikely that this gap would be due to observational bias.


texts: Struggling to understand the phases of the moon

texts:
Source

Typically this diagram is how the phases of the moon are explained but the issue is this, namely, the phases seen on the right half are not possible. All the phases should appear on the left half during the night when the moon is typically most visible.

So how on earth are the phases even generated?

The most remarkable phases are waning moon phases because the moon is lit up on the face away from the sun light source.

What am I missing?

I’ve edited the question by adding two additional photos showing the progression of the moon in the night sky over the course of a given time interval and several days, as well as a synodic month which would hopefully indicate based on the position of the moon the sequence of days and based on the height the time of day/night.

Source

Source

Here is a link to the explanation of how she generated her photo and over what time span but you must have a Facebook account to read it. It is easier to follow the Italian than the English but both are available

Explanation


texts: Is the Big Bang inflation caused by Dark Energy

texts: The rate of expansion of the universe after the Big Bang is described as Inflation. It is stated as being initially very fast then slowed. But the expansion is still continuing.  Some say expansion is currently powered by Dark Energy. The equations unlike gravity say that the rate appears to be linearly proportional to distance, like Hooke's Law for springs. Initially the universe was very small, so if the spring constant is dependent on the size of the universe, could this explain the inflation? What experiment could be devised to test this?


texts: How much matter was ejected when the Solar System formed?

texts:
Assuming the accretion disk model for the formation of the Solar System, the most important problem, according to wikipedia, is "how the material, which is accreted by the protostar, loses its angular momentum."
If angular momentum is conserved, then as our Sun lost angular momentum in formation, excess gas and dust in the disk must have gained angular momentum.  How much matter (if any) reached escape velocity and was ejected from the Solar System?  When compared to the total mass of the Solar System, was this a significant portion?


texts: Fastest recorded apparent motion of a comet or asteroid seen from Earth (degrees/day)?

texts:
If I've done my maths correctly in this answer comet 2I/Borisov (C/2019 Q4) was seen to move about 0.2 degrees in 7 hours, which is almost 0.7 degrees per day.

I'm assuming this is pretty rapid motion for a comet, but I'm wondering if comets (or asteroids) have been observed to move even faster than this relative to the celestial sphere.

Yes I know the speed of apparent motion depends on incidentals like how close the comet happens to pass to the Earth. I'm just wondering if any particular comet stands out as been particularly fast, possibly even difficult to track because perhaps some software didn't allow such a large offset in tracking relative to the stars.

Question: What is the fastest recorded apparent motion of a comet or asteroid, seen from Earth (degrees/day) relative to the celestial sphere?

note: @JamesK's comment reminds me that I would like to exclude meteor tracks. For the purposes of this question the recorded tracks should be produced reflected light, either of the Sun or of radar illumination, and not be something burning up in our atmosphere.


texts: Absolute/apparent magnitude and distance for HIP31978 inconsistent?

texts:
EDIT: I am still following up, but here's the latest response from Wolfram:

  Paclet servers are updated and optimized for each version of
  Mathematica, so I suspect you may be working on an older version which
  we no longer update. Many times we get reports that data from the
  paclet data for version 9 was incorrect, only to find that it has
  already been fixed for version 10.

According to Mathematica and several other sources, the
known information about HIP31978 (also known as "S
Monocerotis" and "15 Monocerotis") includes:

The star system is about 101.06 light years from our own.
The star's absolute magnitude is -2.79 (some sources say even lower).
The star's visual magnitude from our solar system is 4.66.

The star is slightly variable, but not enough to explain
the following discrepancy:

If the star's magnitude at 32.6 light years is -2.79
(definition of absolute magnitude), it would be about 9.6
times fainter at 101.06 light years (it's actual distance
from us). However, that's only about 2.5 magnitudes
fainter, nowhere near enough to bring it down to magnitude
4.66.

What's happening here, and is this a one-off special case,
or does this happen a lot?

For reference, my calculation of the apparent magnitude:

-2.79 - Log[100, (32.6/101.06)^2]*5 == -0.333192


texts: Was is the angle needed to see a glory (a rainbow-like effect) from space off the Earth?

texts:
What positions would the Earth, Sun and viewer need to be to see a glory (a rainbow-like effect) from space?

What position would they need to be in to reproduce this picture?

Source: Gizmodo (NASA via Universe Today)

Related:

https://earthscience.stackexchange.com/questions/16308/rainbow-dynamics
https://space.stackexchange.com/questions/34357/rainbow-space-probe


texts:
What I'm trying to achieve

For a series of realistic renders I am currently working on I am trying to calculate the light level on different celestial bodies, in terms of the luminous flux (in lumens), as this is the parameter used in the rendering software. (as it's made with earth in mind). Specifically, I am now looking to find the luminous flux on Saturn's moon Enceladus.

Thanks in advance for any help provided :)

What I've tried/found so far

Now the solar irradiance is easy to find as lying somewhere inbetween 16.7 and 13.4 W/m^2. However, in order to derive the luminous flux the frequency contents must be known as the luminous flux weights the light by a sensitivity function for human sight.

Wikipedia gives a formula for the luminous flux as

$$\Phi_v = 683.002 \int_0^{\inf}V(\lambda)\Phi_{e,\lambda}(\lambda)d\lambda $$

Where $\Phi_v$ is the luminous flux in lumen, $\Phi_{e,\lambda}$ is the spectral radiant flux in W/nm and $V(\lambda)$ is the luminosity function describing the sensitivity of the human eye to different wavelengths of light (dimensionless).

$V(\lambda)$ was relatively easy to find, but I have difficulty finding the spectral radiant flux $\Phi_{e,\lambda}$ of sunlight at this distance. Can this be calculated from the irradiance?

I did manage to find the solar irradiance spectrum in space at the earth in (W/m^2)/nm, and I assume this could simply be scaled by $R^{-2}$ ($R$ being the distance from enceladus to the sun) to get the same spectrum at Enceladus, but I am not sure how this relates to the spectral radiant flux.


texts: Average amount of annual daylight at any place on earth

texts:
If this is the wrong group please direct me to the correct one.

It seems intuitively obvious that the amount of daylight per annum should be the same for any latitude on earth. For example, 12 hours per day at the equator. The poles have daylight for half the year and darkness for the other half (crudely).

Is there any way to get an answer to this apparently simple question - is the annual amount of daylight the same at any point on earth?


texts: Where exactly does the Moon flip, given that it appears the other way up in the other hemisphere?

texts:
I've read in multiple sources that the Moon appears the other way up in Northern Hemisphere vs Southern Hemisphere. Here is one that explains why: Does the Moon look different in the northern and southern hemispheres?

My question is, where is the line drawn in this case where the moon 'flips'? Is it exactly the equator? I'm not sure if it is, the simple 'thought experiment' in the above link assumes (for simplicity's sake) that the orbit of the Moon is exactly above the equator. According to Wikipedia, the orbit of the Moon is slightly tilted, and our own earth also tilts from time to time. Where does the moon flip exactly? Does it change throughout the year as our earth change its tilt? If so, how? Which are the areas that always see the northern look or the southern one throughout the year?


texts: Could we carve a large radio dish in the Antarctic ice?

texts: Could we carve a large radio dish in the Antarctic ice that could replace the Arecibo Observatory? Could this work, and what would be some potential limitations?


texts: Redshift observation at different wave length

texts: Can one star be observed at different wave length show different redshift ?


texts: Looking for an equation that describes how star (x,y,z) positions are affected by expanding universe

texts: I understand that coordinates of stars are in RA,DEC. I am looking for a mathematical expression that describes how the positions of stars change due to the expanding universe.


texts: Does matter accelerate to the speed of light as it approaches the singularity?

texts:
$$v_\mathrm e=\sqrt{\frac{2GM}r}$$

If we understand the escape velocity to be the speed needed to escape from the 'surface' of a gravitational object described by the above equation.

It is equally true that the escape velocity is the speed an object pulled from rest will reach when it hits a certain point in the gravitational field.

Since the event horizon is defined as when the escape velocity reaches the speed of light for a black hole, would matter accelerate near the speed of light as it approaches the singularity? Accretion disks are known to move at relativistic speeds near the event horizon, but perhaps oddities occur beyond this point?

The event horizon can be derived from setting the escape velocity of an object to the speed of light, it is a point of no return. I understand there are better definitions, but this is not really germane to the question at hand. How about from the perspective of another in-falling observer?


texts: Accuracy of calculating the vernal equinox?

texts:
Calculating the exact time of the vernal equinox is essential for many ephemeris calculations. NASA Goddard Institute for Space Studies uses (at least for some purposes) the following, rather short source code:
Function VERNAL (IYEAR)
      Implicit Real*8 (A-H,O-Z)
      Parameter (EDAYzY=365.2425d0, VE2000=79.3125)
      VERNAL = VE2000 + (IYEAR-2000)*EDAYzY
      Return
      End

What that means becomes clear when reading the comment inside the code:

For a given year, VERNAL calculates an approximate time of vernal equinox in days measured from 2000 January 1, hour 0.
VERNAL assumes that vernal equinoxes from one year to the next are separated by exactly 365.2425 days, a tropical year [Explanatory Supplement to The Astronomical Ephemeris].  If the tropical year is 365.2422 days, as indicated by other references, then the time of the vernal equinox will be off by 2.88 hours in 400 years.
Time of vernal equinox for year 2000 A.D. is March 20, 7:36 GMT [NASA Reference Publication 1349, Oct. 1994].  VERNAL assumes that vernal equinox for year 2000 will be on March 20, 7:30, or 79.3125 days from 2000 January 1, hour 0.  Vernal equinoxes for other years returned by VERNAL are also measured in days from 2000 January 1, hour 0.  79.3125 = 31 + 29 + 19 + 7.5/24.

I highlighted the essential part of the quote. We know for sure that this algorithm will give the wrong date of the vernal equinox in the year 5333 when it will be off by more than 24 hours, but I suppose it can already be incorrect earlier if the time stamp for the vernal equinox is close enough to midnight. When would be the first time that this algorithm picks an incorrect day?
My question: Is the above quoted algorithm the most accurate way of calculating the vernal equinox for times far in the future or past? How would you do it accurately for time scales of 1000s of years, say with e.g. for an application for archeology?
PS: WolframAlpha calculates vernal equinoxes in the distant future with giving hours and minutes and without any error bars which seems too good to be true.


texts: Why does the moon not leave its orbit around the earth due to the gravitational force from the sun?

texts:
See additional information below added after the answer to the question.

When the moon is between the earth and the sun, the gravitational force on the moon from the sun is greater than the gravitational force from the earth, hence the moon should continue its path towards the sun instead of staying in its orbit around the earth.

When the moon is at 90 degrees to the earth relative to the sun, the moon is moving almost directly towards the sun and then the gravitational force on the moon from the sun is roughly double the gravitational force from the earth, hence there is nothing to stop the moon's trajectory towards the sun and it should continue towards the sun away from the earth. What makes the moon "turn" back towards the earth and away from the sun at the point where it is right between the earth and the sun when at this point right when it turns, the gravitational force from the sun is roughly double the gravitational force from the earth?

I am aware of the movement of the sun and also of the fact that the moon is moving on a different plane to that of the earth and I don't think that can explain my question above.

Thank you for your time, I would like to understand this situation.

Additional information:

The answer does not address the question, let me explain. Although it is true that the moon orbits the sun as described in the answer, this does not explain why the sun does not pull the moon out of its orbit around the earth.

For an object to change direction a net force has to be applied to it according to Newtons laws. a=F/m applied to the moon from the point in its orbit where the moon gets closer to the sun than the earth is to the sun, shows a force vector on the moon towards the sun applying twice the force as another force vector on the moon towards the earth. This results in a combined net force vector on the moon pointing away from the earth and this net force vector will progressively point further away from the earth and more towards the sun as the moon moves closer to the sun and therefore should pull the moon out of its orbit around the earth and pull it towards the sun.

Newtons laws must be true on the three separate objects; the sun, the earth and the moon in the example above.

I have a Master of Science in Engineering and know my physics. I have some friends who are convinced they can prove that the earth is actually flat and that a search on "flat earth" will prove it, and they have asked me the question in this thread to prove to me that the heliocentric model is not true. I took up the challenge, however when looking at this simple example I have not been able to find an answer that is in accordance with normal physical laws.

I hope somebody can come up with an explanation that is in accordance with physical laws.


texts: If the moon still had a magnetic field how long would have been possible to keep an atmosphere?

texts: Let's assume the Moon had a considerable magnetic field to prevent the atmosphere dispersion caused by solar wind. Given the low gravity of the Moon, how many years would pass before all the gases (of an Earth like atmosphere) would escape its body? Would its gravity be sufficient to trap heavier gases like CO2?


texts:
I was watching the new Cosmos and Neil DeGrasse Tyson said something that made me go hmmm...

He mentioned that the only reason that the Earth did not experience the runaway greenhouse effect like Venus is that life had evolved to the point at which it could feed on carbon and take it out of the atmosphere and deposit it in solid form as limestone.

The question is, if we were to find a planet in the Goldilocks zone, how likely is it that it would be habitable for life without already harboring life?  Would we expect that a similar scenario would have had to taken place on that planet to curb the greenhouse gasses in the atmosphere, thereby turning it into another Venus?  Can a carbon cycle exist without life?


texts: How can the oblateness of Earth impart torque to change the longitude of ascending node of a satellite?

texts:
I've read that you can change the longitude of ascending node of a satellite (i.e. changing the orbital plane without changing the inclination) to change its orbital plane by using the torque imparted by the oblateness of Earth. How does this happen exactly? I mean how does the oblateness of Earth cause a torque induced precession of a satellite?

PS. I think I don't understand how torque induced precession works and that's why I am not able to understand this. So if any of you kind gentlefolk are willing to explain, I thank you in advance.

EDIT: I just came across Nodal Precession. And from what I understood that due to Earth's equatorial bulge, the gravitational force vector is offset from its center, thus producing torque. I can visualize how the longitude of ascending node will change, but can't visualise how will the change in the torque caused by slightly offset gravitational force vector will cause it.


texts: Is the colour of a wave from a far galaxy the same for us as for a galaxy which lies between?

texts:
Because of the expansion of the universe, light from a far galaxy is redshifted. The expansion of the universe will make the wavelength of light longer. But is the colour of such light the same for us, as for an galaxy which is between us and the far galaxy.

I first thought that a further galaxy's speed was higher than ours, but I don't think that's right it is relative. But is the speed of the far galaxy from a view of the further galaxy higher than from our view? I don't think so because the universe is expanding faster the further you look. So for the further galaxy the speed of the far galaxy is less high than from our view because the far galaxy is further away from us.

So is the conclusion right that the colour of the same wave is more red for us on earth than from the further galaxy?


texts: How will the Solar tides affect the Earth's rotation once it is tidally locked to the Moon?

texts:
It is my understanding that the tidal forces of the Moon acting on Earth cause it to slow down its rotation and, because angular momentum is conserved, the Moon's orbit subsequently expands. This continues until the Earth's rotation is synchronous with the Moon's orbit leaving both bodies tidally locked to each other.

However once that happens, how will the tidal forces exerted by the Sun on Earth (which are weaker than the Moon's) affect the Earth's rotation? Would they cause the Earth to start rotating again and thus cause the Moon's orbit to shrink?

P.S. I do realize the Earth is not destined to be tidally locked to the Moon until after the Sun evolves into a red giant, so for the sake of simplicity assume the Earth-Moon system survives unscathed without getting disturbed.


texts: What created the big bang's singularity?

texts: I have heard theories for the big bang like: of another universe existing before the Big Bang, or an unstable white hole that blew up, or our universe detaching from our mother universe, or our universe coming out of a black hole. Most of these theories don't make sense, and I want to know the most-likely-to-be-true theory for how the singularity was made.


texts: What projection would I use to map the northern night sky onto a geodesic dome?

texts:
I'm trying to create a geodesic dome with the stars of the northern night sky inscribed on the outside. The highest point of the dome would be the celestial north pole. How do I create a map that projects onto the "net" of the geodesic dome, such that when I assemble the dome, the stars are in the correct positions? I have an equirectangular map that I have rotated 90 degrees north so it is centered on the pole.

My existing map is a high-resolution jpeg file in an equirectangular projection. I have some experience creating and manipulating panoramic images, but much less experience converting between map projections! I would like to use a computer program to convert this projection into a printable template if possible.


texts: Is it possible to know if you are travelling close to the speed of light if you have nothing to compare your speed with?

texts:
This is a question that has been bugging me for some time. Let's see if I am able to make me understood!

Imagine you are travelling in a spaceship at 99.9999999999% the speed of light and you are somehow within a spaceship without windows.

My question is, is there ANY kind of experiment that would show you any time/space dilation effect as compared to being stationary? Is there ANY lab or thought experiment you could make or think that would tell you there are weird things happening with time and space outside your spaceship? I mean, would physics work differently than they would at home? Would radioactive atoms take longer to decay in a way you could measure and compare with your earth-based decay tables? Anything?

Or the only way to find out would be simply to step out of the spaceship and find out that life on Earth has gone extinct in the last couple of hours?

And another question related to the first. If you were travelling in the spaceship at that speed in the X-axis direction and you handthrew a baseball in that same direction, would that ball's mass or inertia explode asyntotically to practically infinity since you are increasing a fantastically high speed a tiny winy bit more? Or perhaps you could not threw the ball at all because of the huge mass increase being that close already to the speed of light? Or you wouldn't notice nothing special and a regular sized with normal weight baseball would impact the other side of the room at a relative speed to you of 60 km/h?


texts: How do tip tilt mirrors correct distortion in adaptive optics?

texts:
I'm currently trying to learn about how adaptive optics correct the blurriness caused by atmospherical seeing effects. This is my current understanding of how adaptive optics works (trying to offer some context, I have a very limited understanding at the moment).

Wavefronts from celestial bodies become distorted as they pass through the Earth's atmosphere due to variations in refraction indices as they pass through different density air, temperature variations and so on. This distortion as far as I know, causes the wavefront to look squiggly instead of being straight parallel lines. Once the light reaches the telescope, it is reflected off a tip tilt mirror, then reflected off a deformable mirror, then a beam splitter splits the light rays and one half is passed through a computer sampling device which detects distortions in the wavefront. This is done up to a 1000 times per second, and somehow the computer causes actuators fitted at the back of the deformable mirror to move such that the reflected light off the deformable mirror is now undistorted (i.e. the wavefronts are a straight line, not squiggly). Thus adaptive optics fixes the distortion issue.

I have a few questions arising from my current understanding:

What exactly does the tip tilt mirror do to help fix the distortion problem? Wiki simply says that it fixes the problem of aberration but doesn't offer a specific explanation of how.
Why are straight wavefronts ideal when viewing celestial bodies? As in, how does the squiggliness of the wavefronts actually make the images look blurry?

I believe I am asking too many different types of questions in one post, so I'll make a separate post for this last question, but for anyone reading this:

I keep reading that increasing the size of the primary mirror will improve resolution. I have seen justification of this using Dawe's limit such as

  By considering the formula R= 2.1*10^5*wavelength/ D, where R is the minimum angular separation required by two point sources for them to be resolved, so as primary mirror diameter increases, D increases, so R decreases meaning that resolution of the telescope is improved.

I don't really see how they can apply the R=... formula to primary mirrors because I have only seen it derived in the context of light diffracting when it passes through a small slit, and not mirrors (which don't allow light to pass through, but rather reflects it). Can someone explain to me why we can apply this formula to mirrors as well?


texts: Is there a photo that shows a iron meteor or asteroid in space in raw form having no layers of fusion crust?

texts: A raw iron meteor or asteroid in outer space should be in its raw form having no signs of fusion crust from the friction of atmospheric entry and should therefore show distinctive signs like the posted image.


texts: Why does gravity make time go slower and warp light?

texts:
I know that objects with lots of gravity are capable of warping light or slowing time (an example being a black hole). I also know this is because of the theory of relativity, but I need someone to expand on that and explain why/how that works.

Also, please write the answer in somewhat simple terms, as I am not (yet) an expert on this stuff :)


texts: A star a black hole and planets around them

texts:
Imagine we have a black hole and a star.

There are very close to each other so black hole slowly consumes the star.

It is possible to have planets in this system, and for them not to be consumed by this black hole but just follow their unique orbits. Could there even have life there?


texts: Can anyone provide a list true source (ancient and contemporary) for the ancient Greek astronomy?

texts:
Although there is a lot of work published in last century or so on greek astronomy but I am seeing those to be biased in many ways.
I am trying to find what is the archeological or actual contemporary source of greek astronomy rather than translations to Arabic.
Can anyone provide me with the list of Arab translations of ancient Greek works?


texts: Temperature of the intracluster medium (ICM)

texts:
I've read once in an article that the temperature of the medium within galaxy clusters (the intracluster medium or ICM) is extremely high.

What does that temperature really mean? Particle velocity?
Why is that so?
Is that medium the "Void"?
Is it in conflict with the CMB temperature (that's about 3 K)?


texts: Calculating angle between the sun and a perpendicular to earth given lon/lat & time

texts:
If you had your longitude/latitude, and the time/date, how could I go about working out the angle between your normal and the sun?

At first I was doing a simplistic approach of assuming elliptical orbit in only two dimensions and that the earth is a perfect sphere,

Can I get a more accurate method /formula than this that can be evaluated in one step without any iterative methods?

Here is rough example of what I mean, say the green plane is the point on the surface of the earth I want.

The angle I seek is between the black line perpendicular to the green plane and the black line between the plane and the sun.

There are 2 problems involved here, knowing how the normal changes as the non spherical earth rotates and knowing the relative position between the earth and the sun.
Any help appreciated.


texts: How do you estimate the error on the height/width of a Gaussian?

texts:
I'm trying to fit Gaussians to several lines in a spectrum that I have. Some of them overlap with one another, causing the fitting program that I'm using to not be able to give reasonable estimates for the errors on the measurements. For example, sometimes it will give the width of the spectral line to be 0.5 GHz but give the uncertainty at 1,000 GHz.

To fix this, I've been doing manual estimates on the ones that it can't get. I read that you can estimate the error on the peak of the Gaussian with:

Peak Error = (1/2)*(Width / Signal To Noise Ratio)

but I can't find anything for the height or width. Are there similar ways to estimate the uncertainty on these measurements?

Thank you.


texts: How thick or deep does solid carbon dioxide accumulate on Mars?

texts:
On Mars is there an area in which all the $CO_2$ evaporates exposing dirt near the pole? How deep can solid $CO_2$ accumulate during winter in that area during the Martian Winter?

https://space.stackexchange.com/questions/31724/solar-carbon-dioxide-collector-on-mars


texts: I have always wondered how Jupiter and the other gas giants worked when it came to having a core(If they have one). Would it be rocky or liquid, or can it be a gas. Every time I have asked this question to my teachers I have never gotten an exact answer.


texts: Moving-Cluster method for determination of the distance of Hyades. A starter problem

texts:
I am currently following a class of observational astronomy lab. I will present a brief description of the method in first and then proceed to the question, so anyone is welcomed to read the entire post or move directly to the problem. The current question is about the Moving-Cluster method, for which I quote from Wikipedia

  In astrometry, the moving cluster method and the closely related convergent point method are means, primarily of historical interest, for determining the distance to star clusters. They were used on several nearby clusters in the first half of the 1900s to determine distance. The method is now largely superseded by other, usually more accurate distance measures.*

One can find more here http://pages.uoregon.edu/soper/Stars/movingcluster.html . A brief description of the method is like that:

From photographs taken, say, 10 years apart, we can see that a star of the cluster has moved. (It has proper motion.) Let us suppose that the proper motion is an angle μ. Then the angle θ is the angle between the convergent point and the star or equally the angle between the radial and tangential speed of the moving star

If one knows the angle θ, he/she will be able to find the movement of the star and in the end, calculate it' s distance, through deduced relations beginning with $ v_t =v_r \tan θ.$

Question
I know the declination and the right ascension of both the star and the convergent point.

My problem as is to find the angle θ. In the exercise I have it is requested to find the angle between the star and the convergent point, that is θ , using spherical trigonometry. My mind goes on to using the cosine relationship:

$$ \cos a = \cos b \cos c + \sin b \sin c \cos A ,$$ for the triangle

But, although it may be simple, I cannot understand where this triangle is to be implemented. What are it' s angles in my problem. Wherever I have looked, the angle θ is taken as granted.

So, should I use something like the triangle? If yes, what the triangle should be? Should the Sun be on one angle as the image above with the convergent point? Should I define another triangle? In the end, for whatever triangle I have thought, how will I calculate the needed sides? Note that I know the right ascension and the declination of both the convergent point and the star's.


texts: How far apart are stars in a binary system?

texts:
I'm wondering how far apart from one another the stars are in binary systems.
What is the distribution of the separation between binary stars? Are most of the binary stars very far apart like Sirius (8.2 to 31.5 AU)? Are there many stars in orbits even wider? Are there more pairs with grazing orbits?

Is there a database similar to exoplanets.org where I could see the distance between the pair of stars for all the binary systems we know of?


texts: So I got this information from a magazine , Scientific American issue Physics at the Limits. The theory is that our Universe came about, when in the "Bulk Universe", which is four dimensional, a four dimensional Star collapsed and formed a black hole which became our 3 dimensional "Brane Universe", in which we live. My question is, how could this one Star have contained all the material that is in our Universe ?


texts: Would an exoplanet without axial tilt have no seasons?

texts:
Would an Earth analog exoplanet which rotates around a solar analog, but without axial tilt, have no seasons?

Would it be similar to how Los Angeles does not have very noticeable seasons compared to other parts of the Earth?


texts: Recommendation for introductory cosmology text

texts: I am looking for recommendations for an introductory text (or texts) on cosmology on the advanced undergrad or beginning grad level. I am coming from primarily a physics undergrad background (doing some undergrad research on galaxy Lyman-alpha emission and attending some of my institution's astrophysics journal club meetings) and will beginning a graduate astrophysics program in the fall. I am looking especially for texts that also provide a good introduction into GR since I have never had a chance to learn GR formally.  I have had a lot of experience with Lyman-alpha radiative transfer and some experience with large-scale structure and baryon oscillation, if there are any books that can play off those strengths.


texts: How well can the Sun's surface be resolved by an observatory?

texts: There's no lack of photons, how well could a telescope resolve Sun spots and other surface features of the Sun? How would a high resolution Solar (space) telescope differ from for example Hubble which avoids the Sun by a 50° angle or so?


texts: How did Astronomers deduce that the Sun was not a ball of fire?

texts: Its common knowledge that people used to think that the sun is a ball of fire or molten metal, but when did science start to prove otherwise?


texts: How can I id this celestial without data?

texts:
Anecdotal. Also, I'm using the term 'celestial' loosely; to mean something shiny in the skies.
I'm based out of Nagpur in Central India. Sleeping outdoors on account of summer over the last few days I've made a weird observation. No matter what time it is, there is a fairly bright body visible in the NNW skies at an elevation of perhaps 20 degrees. From what little I gather a GSO object would be really dim, or even invisible. A LEO couldn't be in GSO unless it was in powered flight. I'm utterly flummoxed. The only reason I haven't seen it before is because earlier in life I would sleep outdoors on the balcony where this particular field of view is blocked by other structures around. Sleeping on the ground floor there is a field of view not available on the first floor. Adjacent buildings blocking the view on the first floor also act as a reference that the position of this object has not changed no matter what time of the night it is.
My location (from Google Maps) is 21.17103958702249, 79.08452532230748
The general direction where this object is visible is due 21.171644779275333, 79.08410335986589
How can I id this object?


texts: When the sun explodes, will some of the planets in the Solar System survive and become rogue planets?

texts:
Say if a large enough star, that has a number of planets, were to explode in a supernova:

Would any of the planets survive?
Would they become rogue planets?


texts:
In the movie, First Man Neil Armstrong and his colleague David Scott, as part of the Gemini 8 program, attempt to dock with the Agena. But it turns out to be disastrous as they go into a continuous roll over.

My question is:

What is the need for docking with the Agena and then later undocking so as to land on the moon in a smaller vessel? Why can't there be one rocket which takes the passengers, lands as a single unit and then comes back (much like how an airplane is) without docking and undocking? Wouldn't that be easier?
What caused the continuous roll over and how did the RCS Brakes help in the stabilization of the vessel?


texts:
So I'd like to ask whether the semi-major axis of planetary orbits are aligned? Logically, they shouldn't be, but many websites act as if they are. If they're not aligned, what's the angle between the reference xy axis and the semi-major axis of the orbits of planets?

Thanks!


texts: I recently saw the International Space Station without a telescope. Are there any other man-made space objects that can be seen using bare eyes?


texts: How Are Radioactive Decay Rates Influenced by Neutrinos - On Earth and Other Dense Planets

texts:
I read a science report recently that mentioned an accidental discovery where radioactive decay rates shifted slightly slower in advance ( about a day and a half) of solar storms or in sync with sun's 33-day pattern/rotation of the sun's core. Seems that neutrinos emitted from within the sun or at surface of the sun arrive in advance of other wave/particle radiations AND effect earthly atomic natures.

Aside from predicting solar flares/storms, does this imply decaying atoms/elements absorb or block neutrino emissions to any substantial degree that might of use in other areas of science?


texts: Is diffuse energy distribution considered in the galaxy rotation curve explanations?

texts:
Problem number 23 in chapter 1 of Purcell's "Electricity and Magnetism" Second edition page 37 shows that 90% of the energy stored in the electrostatic field of a spherical charge distribution of radius R is contained in a spherical region of 10R.

The energy by this description is diffuse and only partially resides within what we would call the physical bounds of the particle. Gravity has the same form as the electromagnetic force and I would expect would have this same character of distribution of energy (i.e. 90% of the energy of the gravitational mass contained within a radius of 1R is stored within a sphere of 10R).

Is this true of gravitational energy and has this little detail been considered in the galaxy rotation curve explanations? I would think that something this elementary would be well accounted for in galaxy rotation descriptions. Much of the electromagnetic and gravitational energy seems diffused into the area surrounding mass and I think that galaxy rotation curves require more diffuse gravitational energy distribution don't they?


texts: Rocket Equation from Newton’s 3rd Law, Force of Gravitation, and dp/dt

texts:
I am using the derivative of momentum (dp/dt) with Newton’s 3rd Law with the gravitational force of Earth.

$$
F - F_{gravity} = \dfrac{\mathrm{d}p}{\mathrm{d}t} \\
F - \dfrac{G \, m_e \, m_r}{r^2} =  v  \, \dfrac{\mathrm{d}m}{\mathrm{d}t} + ma\\
$$

$F$ = Force created by fuel (at time t)

$G$ = Gravitational Constant

$m_e$ = Mass of Earth

$m_r$ = Mass of rocket (at time t)

$r$ = Distance between Earth and rocket (at time $t$)

$v$ = Velocity of rocket relative to Earth (at time $t$)

$dm/dt$ = Instantaneous rate of change of mass of rocket (at time $t$)

$m$ = Also mass of rocket (at time $t$)

$a$ = Instantaneous acceleration of rocket (at time $t$, equal to $dv/dt$)

Is my equation correct for a standard rocket? Would dm/dt be negative as the rocket is losing mass over time?


texts: Are we still going to have rainbows if Sun is replaced by another star?

texts: Rainbow is a property of light splitting due to the water molecule present in the clouds and is related to the light emitted by our Sun. Our sun is a yellow star. Now if we replace sun by a blue giant star or red giant star, or any other star of different color, are we still going to have rainbows? If yes is it still going to compose of seven colors? What kind of possible change will occurs, if any?


texts: any unique phenomenon when the cores of two planets are aligned with their star's core?

texts: Imagine a line passing through the cores of two planets (in the same planetary system) and their star. Have we ever witnessed this - either with both planets on the same side of the star or on opposite sides? If so, was there a unique phenomenon associated with the event?


texts:
The speed of light in a vacuum is presumably the fastest speed possible.

if gravity bends the course of light, does this imply that gravity the retards light so it is moving at a slower speed?  If it affects its course, why cannot gravity affect its speed -- or does it?

And if gravity does affect the speed of light, what does that say about our measurements of the distance to the farthest observable object?  Could we assume that all the gravity effects across 15 billion light-years even themselves out?  Or is the actual distance across the observable universe subject to unknowable variations due to gravity effects?